What is the ruling on alerting the Imam by saying "Subhan Allah" twice if he forgets the first Tashahhud? Is it permissible to alert him with this remembrance if the intention is to alert the Imam, or must the intention be its true meaning?

It is permissible to alert the Imam by saying "Subhan Allah" (Tasbih) if he makes a mistake, and this does not invalidate the prayer according to the majority of scholars, including Al-Awza'i, Al-Shafi'i, and Ishaq. Some Shafi'i jurists held that intending only to alert without intending remembrance invalidates the prayer; therefore, it is better for the worshipper to intend both remembrance and alerting simultaneously. Repeating Tasbih does not invalidate the prayer, and it is sunnah to repeat it until the Imam takes notice.